Colossendeis melancholicus Stock 1974

Colossendeis melancholicus Stock, 1974.

Plate 5C, D

Colossendeis melancholicus Stock, 1974: 988 –990.— Staples, 2007: 79 –94.

Colossendeis rostrata Turpaeva, 1994: 91 –96 (new synonymy).

Material examined. One specimen (NHMUK 2018.36), Southwest Indian Ocean, Atlantis Bank, 32˚ 43. 20'S, 57˚ 15. 39'E, parent no. 2615, 1117 m, specimen JC066-3846, stn event 8.5, 10 December 2011. One specimen (NHMUK 2018.37), Southwest Indian Ocean, Atlantis Bank, 32˚ 43. 20'S, 57˚ 15. 39'E, parent no. 2615, 1117 m, specimen JC066-3847, stn event 8.5, 10 December 2011.

Distribution. Grand Bahama I., West Atlantic Ocean; off Jamaica, Caribbean Sea, (unpublished); Tasman Sea (west coast Tasmania); Gulf of Guinea, East Atlantic Ocean; Southern Ocean, Southwest Indian Ridge. 500–1755 m.

Remarks. The leg span of the largest specimen here is about 54 cm and the other about 47 cm. Colossendeis melancholicus is a distinctive species on account of the proboscis length which approaches three times the trunk length, here 2.9 times in the larger specimen and 2.8 times the trunk length in the smaller specimen. The proboscis lengths are about 16 and 14 times their greatest widths respectively. The proboscis is very slightly inflated at about 45% of its length. These specimens are larger than specimens collected previously but agree with the holotype in all significant respects; in particular they agree in all proportions and share the characteristic long, curved proboscis. The length of the tarsus varies between legs in the same specimen from being equal to the propodus length to being almost two times. The first legs are shorter than the second legs but also vary in length within and between specimens from not reaching the distal margin of tibia 2 to one-third the length of the tarsus. Live specimens are uniformly orange in colour (Plate 5C) and were observed mostly on vertical cliff faces on the Atlantis Bank in association with pink, four-lobed anemones (Isactinernus quadrilobatus). They were also observed on open seabed with no direct associations apparent although the same species of anemone was common in the area. One specimen on a vertical rock face was seen with its proboscis inserted deep inside the anemone (Plate 5D) but whether this pycnogonid was feeding on the gut contents of the anemone or body tissue is not known. No obviously dead or atrophied anemones were apparent at the site. On the basis of deep-sea images posted on the internet this species has a much wider distribution than is presently understood. This is the southern-most record of this deep-sea species.

Turpaeva (1994) appears to have been unaware of Stock’s C. melancholicus from which her species C. rostrata Turpaeva, 1994 collected from the Gulf of Guinea is indistinguishable. These species are synonymised.

Distribution Florida Straits, Caribbean region, South West Indian Ridge, Gulf of Guinea and off Tasmania. 500 m to 1755 m depth.